iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

perf/x86: Fix filter_events() bug with event mappings

Browse Source 
commit 61b87cae6361ea6af161c1ffa549898892707b19 upstream.

This patch fixes a bug in the filter_events() function.

The patch fixes the bug whereby if some mappings did not
exist, e.g., STALLED_CYCLES_FRONTEND, then any event after it
in the attrs array would disappear from the published list of
events in /sys/devices/cpu/events. This could be verified
easily on any system post SNB (which do not publish
STALLED_CYCLES_FRONTEND):

	$ ./perf stat -e cycles,ref-cycles true
	Performance counter stats for 'true':
              1,217,348      cycles
	<not supported>      ref-cycles

The problem is that in filter_events() there is an assumption
that the argument (attrs) is organized in increasing continuous
event indexes related to the event_map(). But if we remove the
non-supported events by shifing the position in the array, then
the lookup x86_pmu.event_map() needs to compensate for it, otherwise
we are looking up the wrong index. This patch corrects this problem
by compensating for the deleted events and with that ref-cycles
reappears (here shown on Haswell):

	$ perf stat -e ref-cycles,cycles true
	Performance counter stats for 'true':
         4,525,910      ref-cycles
         1,064,920      cycles
       0.002943888 seconds time elapsed

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: jolsa@kernel.org
Cc: kan.liang@intel.com
Fixes: 8300daa26755 ("perf/x86: Filter out undefined events from sysfs events attribute")
Link: http://lkml.kernel.org/r/1449516805-6637-1-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Stephane Eranian 2015-12-07 20:33:25 +01:00 committed by Greg Kroah-Hartman
parent f7766d1fdf
commit 0554b4d5dd
1 changed files with 10 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/x86/kernel/cpu/perf_event.c
View File

@ -1550,6 +1550,7 @@ static void __init filter_events(struct attribute **attrs)
{
struct device_attribute *d;
struct perf_pmu_events_attr *pmu_attr;
int offset = 0;
int i, j;
for (i = 0; attrs[i]; i++) {
@ -1558,7 +1559,7 @@ static void __init filter_events(struct attribute **attrs)
/* str trumps id */
if (pmu_attr->event_str)
continue;
if (x86_pmu.event_map(i))
if (x86_pmu.event_map(i + offset))
continue;
for (j = i; attrs[j]; j++)
@ -1566,6 +1567,14 @@ static void __init filter_events(struct attribute **attrs)
/* Check the shifted attr. */
i--;
/*
* event_map() is index based, the attrs array is organized
* by increasing event index. If we shift the events, then
* we need to compensate for the event_map(), otherwise
* we are looking up the wrong event in the map
*/
offset++;
}
}